Joseph Young had 18 points for the Ducks (18-8, 6-8 Pac-12), who appear to be getting back on track after a midseason slump.
It was the third-straight win for Oregon, which started the season 13-0 before losing eight of its next 10.
Sunday's win took some work, however, as the Ducks had to overcome a 31-24 halftime deficit and the absence of Damyean Dotson, who didn't play after starting 60 straight games.
Former Curtis High School star DaVonte Lacy scored 19 to lead the Cougars (9-18, 2-13), and D.J. Shelton had 14 points and 10 rebounds.
Washington State shot 27.3 percent in the second half, making just 6 of 25 attempts from the field. The Cougars were also 6 for 22 from the 3-point line.